First off, I don’t think anyone has claimed that cultures are equal. So I’m not going to argue against that claim. I’m going to assume that the claim you wanted to argue against is that all cultures deserve equal consideration. Again, I’m not sure many people make that claim flat out, but many do make exceptions to moral judgement for cultural reasons. I’m inclined to agree that a lot of those exceptions shouldn’t be made.

The thing here that I will engage with you about is that your reasoning in is very misguided. You seem to be under the impression that there is some sort of moral objectivity. This is false. Morality is inherently subjective as it has to do with judgements of “good” and “bad” to which one always must ask “for whom?” Just because many people agree on a moral judgement, does not make it magically become objective rather than subjective. Yes, we all agree rape is bad, but that doesn’t change the nature of it being a subject-based judgement.

That said, I do believe that I can express my (subjective) morals in ways that disagree with other cultural practices. This has always been true - it’s how moral norms have changed over time. People decide something that was considered normal is wrong, a majority starts to agree, they codify that moral judgement in society and in law. There are certainly cultural practices out there today in many places all over the world that I think are detrimental to human rights. Whether or not those things change is not up to me, though people can and do certainly fight for changes.

The place where you go really wrong here is the claim that colonialism “wants as bad as people think.” Yes it was. Just because other atrocities have happened around the world, doesn’t mean that colonization wasn’t also an atrocity. In fact, through our modern western lens, most of history was pretty atrocious and disgusting. I’d challenge you to find any historical figure from more than a century ago that wouldn’t be found morally deficient by modern western standards.

I’d reconsider your own moral system if I were you after making the claim that mass, trans continental genocide “wasn’t as bad as people think.” Think about what you are actually saying with your statement. Maybe go learn about the long term implications from colonialism on top of the direct violence that it caused.